Restore ld_bfd finding libgcc to link with it, fix bootstrap build for linux-armhf

[illwieckz]

Restore ld_bfd finding libgcc to link with it, fix bootstrap build for linux-armhf.

Fixup for:

• Allow building with Clang without installing GCC #26

Fixes:

arm-linux-gnueabihf-ld.bfd: nacl_bootstrap.dir/nacl_bootstrap.c.o: in function `iov_int_string':
nacl_bootstrap.c:118: undefined reference to `__aeabi_idivmod'

[slipher]

How are you using it? It works for me in the Scons build for both GCC and Clang. With Clang (scons --mode=opt-host,nacl saigo=1 werror=0 platform=arm all_programs -j9) the command issued is:

env CXX='/usr/bin/clang++' /usr/bin/python3 /unv/nacl/src/trusted/service_runtime/linux/ld_bfd.py --compiler arm-linux-gnueabihf-g++ -m armelf_linux_eabi --build-id -static -z max-page-size=0x1000 --orphan-handling=discard --defsym RESERVE_TOP=0x40002000 --script /unv/nacl/src/trusted/service_runtime/linux/nacl_bootstrap.x -o scons-out/opt-linux-arm/obj/src/trusted/service_runtime/nacl_bootstrap_raw scons-out/opt-linux-arm/obj/src/trusted/service_runtime/linux/nacl_bootstrap.o

With GCC (scons --mode=opt-host,nacl saigo=1 werror=0 platform=arm all_programs -j9 --no-clang) the command issued is:

env CXX='arm-linux-gnueabihf-g++' /usr/bin/python3 /unv/nacl/src/trusted/service_runtime/linux/ld_bfd.py --compiler arm-linux-gnueabihf-g++ -m armelf_linux_eabi --build-id -static -z max-page-size=0x1000 --orphan-handling=discard --defsym RESERVE_TOP=0x40002000 --script /unv/nacl/src/trusted/service_runtime/linux/nacl_bootstrap.x -o scons-out/opt-linux-arm/obj/src/trusted/service_runtime/nacl_bootstrap_raw scons-out/opt-linux-arm/obj/src/trusted/service_runtime/linux/nacl_bootstrap.o

Anyway surely you don't need this junk? It was described as only being needed to avoid using gold but that hardly exists any more. I would have gotten rid of it but didn't feel like untangling everything at the moment. For a new build surely you could just set it in the toolchain file or whatever.